1. Technical Field
The present invention is directed to media drives. More specifically, the present invention is directed to a method and apparatus for isolating and attenuating shock and vibration in a disk module that includes media drives that are mounted on a printed circuit board (PCB).
2. Description of Related Art
High performance disk drives are finely tuned electro-mechanical devices. The precision necessary to allow these devices to work is proportional to their capacity to hold customer data and their ability to handle the data in volume. Disk drive performance is dependent on the vendor's drive design that includes the servo algorithms, spindle and disk pack balancing, internal damping and dynamic characteristics. Disk drive performance is also influenced by the environment in which it must operate.
In an effort to reduce cost per megabyte of storage, the track density, or tracks per inch (TPI), have increased. The TPI trend, along with efforts to reduce packing costs and unit footprints, has led to significant challenges regarding disk drive implementation. Obstacles presented to the industry consist of damping and attenuating the disk drive's own internally generated vibrations, isolating the disk drive from vibrations created by neighboring disk drives, and isolating the disk drive from externally generated shocks and vibrations.
A poorly implemented disk drive mounting solution may cause various problems at a higher system level. An unconstrained, vibrating disk drive will tend to knock itself off track while performing a read or write seek. If the drive cannot successfully find the correct location to read or write on the disk surface, the disk drive must wait until the disk pack rotates around to the same location to attempt the operation again. The extra rotation results in a write or read inhibit that is treated as an error. These errors can affect the input/output speed of the individual disk drive and the system as a whole. If the problem is severe enough, the disk drive will be turned off or fenced due to its inability to read and write data. It is possible that the disk drive will be fenced due a system level mounting problem and not due to a problem with the disk drive itself. Corrective maintenance for shock and vibration induced errors will usually result in the replacement of a healthy disk drive.
Several approaches have been used in attempts to minimize the effects of self-induced vibrations, and externally induced shocks and vibrations on various disk drives. Many of these same approaches are also used with other moving-media type drives such as optical dives, magneto-optical drives, and tape drives, generically referred to as media drives.
A common shock and vibration damping approach is to attach each media drive to a system level drive tray through one or more springs. Springs provide a degree of mechanical isolation between neighboring media drives mounted in the drive tray, as well as isolation from externally induced shocks and vibrations. Springs, however, allow vibrational energy to remain in the media drive thus adding to the energy spectrum of the media drive environment. Springs also contact the media drive chassis in only a few specific locations that are selected based upon a center of mass and not based upon closeness to the vibration sources.
One method of mounting multiple media drives in a drive module is to attach the drives to a printed circuit board (PCB). The assembly of the drives mounted on the PCB is referred to as a drive module or a “blade”. Drives mounted on a PCB disturb each other while seeking. Vibration is transmitted through the PCB, and any other rigid mechanism attached to the drives. Average performance losses of over 40% are seen due to the coupling of vibration from a seeking drive to a neighboring drive performing writes.
FIG. 1 is a perspective view of a drive module assembly 10, also referred to as a “blade”, that includes a plurality of media drives secured to a single PCB and that utilizes a single solid rail for reinforcing the assembly in accordance with the prior art. Multiple media drives 12a and 12b are mounted on a single PCB 14. A single solid stiffening rail 16a is secured to the single PCB 14 and along a top side of both media drives 12a, 12b in order to reinforce the entire blade assembly 10. A second single stiffening rail 16b is secured along a second side of both media drives 12a, 12b to provide additional rigidity to blade 10. Each rail 16a and 16b is formed from a single piece of a material such as sheet metal. While this stiffening rail succeeds in reinforcing the rigidity of the blade assembly, the single rail also provides an efficient means for transmitting vibrations from one media drive to another.
Therefore, a need exists for a method and apparatus for isolating and attenuating shock and vibration in a disk module that includes media drives that are mounted on a printed circuit board (PCB).